Ultra-small noble metal nanoparticles (NPs) have become a central topic in nanoscience and catalysis due to the significant differences between the properties of NPs compared to bulk metals. One material exhibiting this behavior is gold, which is inert as a bulk material, yet when prepared as ultra-small NPs, displays remarkable catalytic activity. For example, gold nanoparticles (AuNPs) have been shown to catalyze a variety of reactions including oxidations, reductions, and carbon-carbon bond formation.
Because of the importance of active site availability in heterogeneous catalysis, prevention of particle aggregation can play a significant role in maintaining catalytic efficiency. During catalytic reactions, reactants compete for active surface sites, potentially displacing ligands and eventually leading to unstable high energy surface sites. This, in turn, can cause particle aggregation, reduce catalytic activity, and limit reusability. One approach used to prevent NP aggregation involves the use of a support material that can be a co-catalyst or simply provide mechanical stability during catalytic cycles. Porous and nonporous silica has been widely used because of the ease of modification of the silica surface with mercapto or amino functionalities, which serve as anchor groups for NP attachment. However, the stability of silica-based materials can be compromised in some chemical environments, leading to nanoparticle aggregation and dissolution of the silica support material. Due to such limitations, polymer-supported AuNPs are attractive because in aqueous media they offer significant stability not available with silica supports. However, many reactions require the use of organic solvents where polymeric supports such as polystyrene can swell and dissolve. Thus, depending on the particular application, limitations regarding such supported nanoparticles remain.